I discovered a neat pattern: using join with the function arrow ((-)) as a Monad. When you join over functions, you get: This lets you pass the same argument twice:

I discovered a neat pattern: using join with the function arrow ((-)) as a Monad. When you join over functions, you get: This lets you pass the same argument twice: once to determine what to do, and another to actually do it. In , we have validators with the signature